In nuclear power reactors, the nuclear fuel typically comprises elongated rods containing nuclear fuel pellets such as uranium oxide and/or plutonium oxide within a sealed cladding. A number of the fuel rods are grouped together to form a fuel bundle. Each fuel bundle is typically open-ended at its top and bottom to form a flow channel. Thus, coolant flows upwardly through a lower tie plate, through the spaces between the fuel rods and outwardly through an upper tie plate, the water being heated during its flow to produce steam, for example, for driving turbines.
The spaced fuel rods supported between the upper and lower tie plates are maintained in a predetermined array and are maintained in spaced lateral relationship relative to one another by a plurality of spacers. The spacers are vertically spaced one from the other along the length of the vertically extending fuel bundle. Because the fuel rods are long and slender, i.e., have a very small diameter on the order of less than 1/2-inch, and are laterally spaced one from the other in the fuel bundle only a small fraction of an inch away from one another, it is essential to restrain the rods from lateral bowing or vibrating during operation. Fuel rod spacers are provided for this purpose and are well known in the art.
Conventional spacers are designed essentially to satisfy certain thermal hydraulic performance criteria, typically without regard for simplicity and ease of manufacture. This has oftentimes resulted in excessive manufacturing costs. For example, current boiling water reactor unit cell spacers are manufactured from individual cells, each associated with one fuel rod position within the bundle. This requires at least one part for each fueled, latticed position. Consequently, a substantial number of parts are required for the fabrication of each spacer, with resultant increase in manufacturing costs and handling. It is therefore desirable to reduce the cost of spacers, and facilitate their manufacturing process, while simultaneously maintaining the structural, nuclear and thermal hydraulic performance capabilities of the prior spacers within the fuel bundle.